The change from centralized, batch operation of computer systems to distributed, interactive usage means more users are more directly involved in these systems. Moreover, computer users are becoming more heterogeneous as the usage of computers spreads. The level of experience or knowledge of the users varies widely. More and more, the use of a computer or data processing system is by nonprofessionals in the data processing arts, and it is therefore important that the system be made user "friendly" to facilitate proper data entry and processing.
User "friendly" systems have typically adopted a display screen "menu" or dialog approach which gives the user a choice of several options to perform and/or blanks to fill in. The blanks correspond to data fields, and these data fields may have constraints on the type of character that will be accepted, the length of the field, the compatibility of one entry with another, and so forth. If data not meeting the constraints is entered at the requested locations, the computer will indicate an error. Often, the nature of the error and the way to correct it will be obvious to the user. However, there are many times when the user, when told that his data entry is incorrect, will not be sophisticated enough to be able to recognize the nature of the error or how to correct it.